The rare penny is made of copper with a small silver plug at its center and was produced as an experiment by the US Mint, which axed the penny before it went into mass circulation, deeming it too large and heavy for practical use.

Todd Imhof of Heritage Auctions said that the coin bears the inscription 'Liberty Parent of Science & Industry', rather than today's 'In God We Trust'.

"At the time, industry and science reflected an enlightenment mindset," he added. "People believed freedom of thought and industrial growth would bind and unify the new country, not religion or God.

"With collectible items, for an item to sell for over a million dollars, it is an unusual event."

An anonymous collector, who had owned the penny for ten years, sold the coin.